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Re: How can I install DOS without a floppy drive?

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In article  <KJFVMLG240577.0769212963@reece.net.au>
           remailer@reece.net.au "Kulin Remailer" writes:

> > Do you have anything odd or excessively modern in your hard drive setup?
> 
> I don't think so, but...
> 
> > DOS 5 doesn't support FAT32 and won't support a partition larger than
> > slightly under 2G ... And it accesses the drive through C,H,S addressing,
> > which can't support a cylinder larger than 1024.
> 
> I'm really not sure how I set up my emulated DOS except for DRDOS 7.03 is
> happy with a 2 gig drive and calls it FAT16B > 32M. I *thought* I gave my
> MSDOS 6.22 system 2G also but fdisk on it only shows me 1G.
> 
> > For many systems, the combination of FAT16 and CHS addressing results in
> > a maximum usable partition size of just under 512M (Depends on how your
> > BIOS translates larger drives to this interface). I believe it is possible
> > to get DOS to work in LBA ... but I've never bothered to figure it out as
> > 512M is lots big for anything I do under DOS.
> 
> > And to make matters worse, the partition offset has to be within the 1024
> > cylinder boundary from the start of the drive.
> 
> I am starting to remember this now. My real DOS partition that I stole from
> my Linux swap is 2G and that's how big I built the filesystem...and DRDOS
> and 98SE boot disks can read it fine and so can FreeDOS. But...it's more
> than 1024 into the drive which from your explanation I am wondering if this
> is why fdisk on the real drive either fails or on DRDOS 7.03 gives me a
> weird partition table that I am afraid to touch. Format failed also, did
> nothing. I was able to exec my autoexec.bat and my system was ok, I just
> can't get the darn thing bootable. It is probably related to what you are
> saying and at this point I have no way to get it on a real box because I'm
> out of space other than my swap files which start about 6-10G into the
> drive.
> 
> > So - when multi-booting older DOS  it's best to make the DOS partition
> > first on the drive, and small.
> 
> Yeah thanks. I had in mind to create 3 2G partitions so I could install
> several DOS but that may not even be possible. I wonder if jacking up the
> numbers so the cylinders are bigger will help or if the limitation is not
> just on cylinders.
> 
> I thought 512M would be plenty too but after I installed only a few DJGPP
> zips and OpenWatcom it was already getting pretty full so I figured I would
> go for the biggest DRDOS would tolerate which seems to be 2G. I'll have to
> plan a little more carefully when I learn the limits of each DOS version.
> 
> > "newer" DOS such as MS-DOS 7 (the DOS under Win9x), PCDOS-7,
> > OpenDOS-7 etc. know how to talk to larger drives may not be so
> > restrictive.
> 
> Yes, it does seem to work better and even run after I booted into it with a
> boot CD and did my autoexec bat after switching to C:. But I didn't check
> to see if MASM/PWB would crash it yet.
> 
> I may look into creating my own boot disk with the full DRDOS install using
> some tools I found on the net. That seems to be the only hope for installing
> on my present setup but because of the CHS stuff that may not work either.
> It will be a little while until I get my old box fixed up. Bummer for me!
> 
> Thanks guys.

Here's an extract from an article around 15 years ago:

| The capabilities of DOS are constrained by a combination of the IDE spec & the
| BIOS. The IDE spec allows for hard disk sizes of up to 130GB, whilst a
| "standard" (non-LBA) PC BIOS can handle disks of up to 8GB in size. The 504MB
| "limit" occurs because of a mismatch between the drive geometries supported by
| each hardware standard. The problem is that DOS uses the "lowest common
| denominator". ie -
| 
|                        BIOS       IDE      DOS
| Max sectors/track       63        255       63
| Max Heads              255         16       16
| Max Cylinders          1024      65536    1024
| 
| To calculate sizes from Sectors, etc, use the following formula :
| 
| sectors x heads x cylinders x 512 = capacity in *bytes*. To convert to MB divide
| your answer by 1,048,576.
| 
| This gives : BIOS limit = 8,032.5MB; IDE limit = 130,560MB; DOS limit = 504MB
| 
| MS-DOS 6.x does *not* support drives up to 2GB natively, unless your BIOS has an
| LBA mode available. It supports *partitions* (important distinction) of up to
| 2GB. Why you'd want a 2GB FAT partition is beyond me, as you'd lose about 300MB
| (ballpark figure) due to "slack" space.

The original message-id is <610520714wnr@naismith.demon.co.uk> but I 
have no idea whether it is still available or not.  Some follow-ups 
(again if they are still available) might be informative:

        <610520714wnr@naismith.demon.co.uk>
        <VRz$dDAIGYNxEwW7@hoskin.demon.co.uk>

In short, DOS can handle up to 2GB; beyond that, you're on your owm 
(though of course things might well have changed in the intervening 15 
years).

Pete
-- 
   "We have not inherited the earth from our ancestors,
    we have borrowed it from our descendants."

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Re: How can I install DOS without a floppy drive? pete@nospam.demon.co.uk - 2011-02-02 20:10 +0000

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